SWITCH PROTECTION ARRANGEMENT

Abstract: A telephone switching network switch protection arrangement has information sent in the form of an information frame through a number of switching units, the information in the frame is re-organised in the switch between input and output and checked for parity by using the V4 byte in the framework before being sent from the switch.

Description: SWITCH PROTECTION ARRANGEMENT This invention relates to a switch protection arrangement in or for a switching network in which information is carried in bit form in a framework in which the framework comprises a plurality of bytes of information each byte comprising in turn a plurality of bits in serial form. The bytes in the framework being assigned titles and references depending on their situation in the framework and the structure of the framework being defined by accordance to standards such as CCITT. Within the framework certain bytes are allocated to the path overhead frame and others to the section overhead frame for data transmission purposes. In order to ensure correct functioning of the switch information, the information to the input of the switch is re-arranged and presented to the output. In this re¬ arrangement the data may be re-written and be corrupted or misrouted and it is an object of the present invention to check for parity of information between the input and the output of the switch. According to the present invention a switch protection arrangement includes a switch, means for establishing switched connections, a plurality of interface cards which include the capability of generating and monitoring multiple test data fields and reporting any discrepancies found, the format of a switched connection including a test data byte which is reserved for transporting a multiplicity of different test data fields which are used to assist in the determination of whether the switch paths are routed and operating correctly and wherein the contents of the data fields comprise: a multiframe synchronisation pattern; a plurality of parity check bits generated from the data carried by that switched connection; the number of the shelf containing the originating interface card of the switched connection; the number of a card position containing the originating interface card; the type number of the originating interface card; and the channel number used by the switched connection to enter the switch. Means may be provided to distribute data to the interface card at the destination of a switched connection; the data containing: the shelf number; the card number; the card type; and the channel number of the source of a switched connection. Means may also be provided to inhibit the reporting of some or all of the detected discrepancies. The test data byte is preferably the V4 byte of an SDH tributary. It is preferred that TU1/2 structured data utilises the V4 byte of the associated path overhead. TU3/AU4 structured data utilises bytes within the section overhead of the frame. The detailed description following is specific to the TU 12 checking mechanism. The same principle of checking is utilised for TU11 , TU2, TU3 and AU4. The TU11 and TU2 also use the V4 byte. The TU3 and AU4 use bytes in the section overhead. Reference will now be made to the four figures of the accompanying drawings to illustrate two embodiments for the use of the invention. In the drawings Figure 1 is an example of a configuration which uses an optical line card to a tributary system and Figure 2 is a system using an optical line card to an optical line card system. Figure 3 and Figure 4 illustrate the location of flags within the SOH for protection. Referring now to the drawings, it is to be understood that the same principles apply to both Figures 1 and 2. A standard framework of information is set up and the V4 byte is monitored. In the system the V4 monitoring is a monitoring system designed to check the connectivity and integrity of the data paths established through the Switch Card(s). In each TU-12 generated internally by an ADMX the V4 Byte contains information about the 'originator' of the TU, and by comparing the received V4 Byte with a record of the 'expected' V4 (configured by the Mux controller) the 'destination' card monitors the integrity of the TU path. The V4 Monitoring is used by the ADMX to detect Switch Card failures and, when dual protected Switch Cards are provided the information from the V4 monitoring is used by the Switch Card Protection System to determine which Switch Card (A or B) to use. The V4 monitoring only operates within the ADMX. The 'external' V4 bytes in the STM-1 going to Line (or STM-1 Tribs) are not specified by the CCITT standard used and are set to all 1 or all 0. The V4 Monitoring is an inherent feature of the ADMX (in all configurations) and it is not possible for the Operator to disable it. The ADMX may be physically equipped and configured in a number of ways. The Line Cards are always STM-1 Cards. The Trib Cards however may be 2Mb/s or STM-1 giving the following possible path connections. Trib (2Mb/s) - Switch - Line (STM-1 ) Trib (STM-1 ) - Switch - Line (STM-1) Line (STM-1 - Switch - Line (STM-1 ) Trib (2Mb/s) - Switch - Trib (STM-1) Trib (2Mb/s) - Switch - Trib (2Mb/s) Trib (STM-1 ) - Switch - Trib (STM-1) In the example of Figure 1 the cards are arranged as an Optical Line Card (STM-1) to a Trib (2Mb/s) card. The V4 Monitoring occurs between an Optical Line Card 1 and Trib Card 2. In this configuration the integrity of a path set up to terminate a VC-12 can be monitored. The TU's are monitored in both directions simultaneously through the Switch. In the Transmit' direction the Trib Card (the originator) inserts the V4 Byte in each TU and is monitored on the optical Mux Card (the destination card). In the 'Receive' direction the Optical Mux (the originator) inserts the V4 Byte and is monitored by the Trib cards (the destination card). The V4 Byte is (under normal working) passed transparently through the Switch. In the second example the Optical Line Card (STM-1 ) transfers to another Optical Line Card (STM-1 ) as shown in Figure 2. TU-12, TU-2, TU-3 and AU-4 can be routed through the Switch, the V4 Monitoring however is only applicable to the TU- 12's and TU2's as path overheads. TU3 and AU4 utilise bytes within the section overhead. See Figures 3 and 4. In Figure 2 the V4 Monitoring between two Optical Line Cards 1 and 3 via a Switch Card 4 takes place. In this configuration the integrity of Paths set up to pass a VC 'through' the ADMX is monitored . The TU's are monitored in both directions through the Switch. The V4 Byte is (under normal working) passed transparently through the Switch. The V4 Byte is inserted into each TU-12 by the Mapping ASIC on the Tributary Card and by the Re-Justifier ASIC on the Optical Line Card. The V4 Byte of each TU-12 contains over a period of four Multiframes (a V4 Byte occurs once per 4 Frame Multiframe) the following information about the originator of the TU. a) Shelf Number b) Card Number c) Card Type d) Channel Number e) Frame Alignment f) Parity Check Parity Check The Parity check bit is calculated over the previous Multiframe (including itself) and set such that the parity is even. Data Format order (read left to right, top to bottom) of the V4 message in the multiframe is as follows:- l-JIVIUL. 1 2 3 4 5 6 . 7 8 (time) V4 Byte #1 P1 0 A1 0 B3 B2 B1 BO (500us) V4 Byte #2 P2 0 A2 0 C3 C2 C1 CO (1.0ms) V4 Byte #3 P3 0 A3 0 0 D6 D5 D4 (1.5ms) V4 Byte #4 P4 0 A4 0 D3 D2 D1 DO (2.0ms) Parity Bits P1 =1/0 P2=1/0 P3=1/0 P4=1/0 (set as approximate) Aliαnment Bits A1=0 A2=1 A3=1 A4= =1 Shelf Number BO=1 B1=0 B2=0 B3= =0 and TvDe Bits Card Slot Card Slot Bits (Type and Number) C3 C2 Cl C Line Card West A 0 0 0 1 Line Card West B 0 0 1 0 Line Card East A 0 1 0 1 Line Card East B 0 1 1 0 Trib Card A 0 0 1 Trib Card B 0 1 0 Trib Card C 0 1 1 Trib Card D 1 0 0 Protection Trib 1 0 1 (The C3 Bit is also referred to as 'Card Type') Channel Number Mapping 63 * 2Mbit/s AU4/TUG-32/TUG-21ATU-12 (CCITT G.709 Multiplexing Structure) D6 TUG-32# Bit 2 (MSB) D5 TUG-32# Bit 1 (LSB) D4 TUG-21# Bit 3 (MSB) D3 TUG-21# Bit 2 D2 TUG-21# Bit 1 (LSB) D1 TU-12# Bit 2 (MSB) DO TU-12# Bit 1 (LSB) Channel Number Mapping 64 * 2Mbit/s AU4/TUG-31/TUG-22 TU-12 (Proprietary Mapping Structures D6 TUG-31# Bit 2 (MSB) D5 TUG-31# Bit 1 (LSB) D4 TUG-22# Bit 3 (MSB) D3 TUG-22 Bit 2 D2 TUG-22# Bit 1 (LSB) D1 TU-12# Bit 2 (MSB) D0 TU-12# Bit 1 (LSB) The system can be used to receive fault detection by monitoring in the ASIC the V4 Bytes, by the Mapping ASIC on the Trib Cards 2 and by the re-justifier ASIC on the Optical Mux Cards, 1 , 3. Each destination card also has stored in RAM complete details of the originator and channel number of each TU that has been routed to it. When a TU-12 Cross Connection is added the V4 Monitoring is enabled and the V4 Byte of each TU is constantly monitored and compared with the stored information to check for V4 faults. Any discrepancy between the 'expected' number and the actual values received by the destination card 5 raised as the following V4 Data Fault Conditions. a) Shelf Number Fault b) Card Number Fault c) Card Type Fault d) Channel Number Fault e) Frame Alignment Fault f) Parity Error Fault The individual fault conditions in V4 faults detected are separately selected (enabled) and combined (OR'ed) to produce a single V4 fault condition for each Switch Card, which, after a suitable persistence check, is reported to an Alarms Processing Sub-system and to a Protection Switching Sub-system ) if Switch Card Protection is in use). The selection of the faults that lead to a V4 Fault condition for the destination cards depends on the System configuration and are shown in the following table. It is necessary to inhibit some faults not only to stop spurious alarms but also to ensure that unnecessary Switch Card Protection Switching does not occur. TABLE System Configuration 1 ' V4 Fault Condition Trib Card 2Mb/s Parity Check enable enable enable enable enable Shelf Number enable enable enable enable enable Card Number enable dis dis dis dis Card Type enable enable enable enable enable Channel Number enable dis enable dis dis Frame Align enable enable enable enable enable STM-1 Trib Card Parity Check enable enable enable enable enable Shelf Number enable enable enable enable enable Card Number enable dis dis dis dis Card Type enable enable enable enable enable Channel Number enable dis enable dis dis Frame Align enable enable enable enable enable Line Card STM-1 Parity Check enable enable enable enable enable Shelf Number enable enable enable . enable enable Card Number enable enable dis Note 1 dis Card Type enable enable enable enable enable Channel Number enable enable enable dis dis Frame Align enable enable enable enable enable * System Configuration V4 Monitoring (No other Protection Mechanism in use) V4 Monitoring when TU Ring Protection is being used. V4 Monitoring when 1+1 STM-1 Protection is being used. V4 Monitoring when Trib Port Protection is being used. V4 Monitoring when Trib Card Protection is being used. A Protection port may be on the same card or on a different card from the one it protects. Only when all protection ports in use are on the same tributary card as the ports they are protecting will the card number be enabled. Many forms of monitoring are required for the V4 Byte depending on the card arrangement. Where an ADMX is operating with a single Switch Card this Switch Card will automatically be selected as the 'working' Switch Card. The V4 Monitoring still operates and the V4 Fault condition shall be reported to the Alarm Processing Subsystem. Protection Switching is not possible. However when the ADMX is operating with Duplicated Switch Cards the V4 monitoring operates and the V4 Fault condition is reported to the Alarm Processing Subsystem and to the Protection Switching Subsystem. The V4 monitoring is one of the criteria used by the Switch Card Protection Subsystem to select the 'working' switch card. When the ADMX is operating with TU Ring Protection it is necessary to disable the Card and Channel Number faults as these may be caused by the action of the TU Protection Switching mechanism operating. When the ADMX is operating with STM-1 Line Protection it is necessary to disable the Card Number faults as these may be caused by the action of the Line Protection Switching mechanism operating. When the ADMX is operating the Trib Port Protection it is necessary to disable the Card and Channel Number faults as these may be caused by the action of the Trib Port Protection mechanism operating. When the ADMX is operating with Trib Card Protection it is necessary to disable the Board Number faults as these may be caused by the action of the Trib Card Protection mechanism operating. When operating with dual Switch Cards, the V4 Faults (A and B) are compared and if a difference occurs for longer than a set threshold period the appropriate Switch Card is deemed to have failed. The Persistence Threshold is configurable by the Operator to be a period of 2,4 7 or 10 Multiframes. The default value is 4. The operation of the V4 Monitoring process requires a number of commands to pass between the Controller Card and Traffic Cards. When a TU-12 Cross Connection is made the V4 Monitoring Configuration detail download and Enabling/Disabling selection download is generated entirely by the ADMX Controller Card. It is not necessary for the Operator to enter any specific information for V4 Monitoring (eg Which Faults to enable), the details of the Cross Connection is sufficient. The V4 Monitoring is only enabled when a particular TU12 Cross Connection is made. Enabling of Monitoring shall apply monitoring to both directions of transmission. When a Cross Connection is set up the Source Cards autonomously insert the required data into the V4 Bytes. The Configuration details for the Destination cards is downloaded from the Controller Card as part of the overall process of configuring a Cross Connection. Details to be downloaded are: a) Originator Card Number b) Originator Shelf Number c) Originator Card Type d) TU Channel Number Depending on the overall system configuration the fault conditions leading to a V4 Fault Condition are Enabled/Disabled as given above. Details to be down loaded are: a) Parity Check Enable/Disable b) Shelf Number Enable/Disable c) Card Number Enable/Disable d) Card Type Enable/Disable e) Channel Number Enable/Disable f) Frame Align Enable/Disable In order to prevent spurious Alarms the Faults are disabled before a Cross Connection is deleted. The default (following a Power-up) for fault enabling on all Destination Cards shall be that all (6) faults noted above are disabled. Enabling shall only be possible once a cross connection has been set up. Figures 3 and 4 to which reference is now made show the location of flags within the section overhead protection. Both figures illustrate the switch diagnostic message used, Figure 3 for AU-4 or TU 31s and Figure 4 for AU-4/3s or TU-32s. Both figures indicate the section overhead bytes and the byte structures used together with the status flags SF or SD to indicate a system fail or degrade flag as appropriate. It will be seen from the above that the information in the V4 byte is constantly monitored and a necessary corrective action is taken. It will be apparent that a number of modifications on the use of the information and its treatment will be possible without departing from the scope of the invention.

Claims: CLAIMS 1. A telecommunications switch protection arrangement including: a switch; means for establishing switched connections; a plurality of interface cards, said cards including the capability of generating and monitoring multiple test data fields and reporting any discrepancies found; in which the format of a switched connection includes a test data byte which is reserved for transporting a multiplicity of different test data fields which are used to assist in the determination of whether the switch paths are routed and operating correctly; characterised in that the contents of the data fields comprise: a multiframe synchronisation pattern; a plurality of parity check bits generated from the data carried by said switched connection; the number of a shelf containing the originating interface card of the said switched connection; the number of a card position containing the originating interface card; the type number of the originating interface card; and the channel number used by the switched connection to enter the switch. 2. A telecommunications switching system as claimed in Claim 1 , characterised in that means is provided to distribute data to the interface card at the destination of a switched connection; the data containing: the shelf number; the card number; the card type; and the channel number of the source of a switched connection. 3. A telecommunication switching system as claimed in Claim 1 or Claim 2, wherein means is provided to inhibit the reporting of some or all of the detected discrepancies. 4. A telecommunication switching system as claimed in Claim 1 , 2 or 3, characterised in that the test data byte is the V4 byte of an SDH tributary.

Inventors: BARKER ANDREW JAMES, CHOPPING GEOFFREY, STONEY DAVID PAUL, BARKER, ANDREW, JAMES, CHOPPING, GEOFFREY, STONEY, DAVID, PAUL
Applicants: BARKER ANDREW JAMES, CHOPPING GEOFFREY, PLESSEY TELECOMM, STONEY DAVID PAUL, BARKER, ANDREW, JAMES, CHOPPING, GEOFFREY, GPT LIMITED, STONEY, DAVID, PAUL
Application year: 1994
Main classification: H04L12
IPC codes: H04J3, H04M3, H04Q11